Re: Enabling Checksums

On 2013-04-13 09:14:26 -0400, Bruce Momjian wrote:
> On Fri, Apr 12, 2013 at 02:38:27PM -0700, Jeff Davis wrote:
> > In general, we have more flexibility with WAL because there is no
> > upgrade issue. It would be nice to share code with the data page
> > checksum algorithm; but really we should just use whatever offers the
> > best trade-off in terms of complexity, performance, and error detection
> > rate.
> > 
> > I don't think we need to decide all of this right now. Personally, I'm
> > satisfied having SIMD checksums on data pages now and leaving WAL
> > optimization until later.
> 
> As I understand it, SIMD is just a CPU-optimized method for producing a
> CRC checksum.  Is that right?  Does it produce the same result as a
> non-CPU-optimized CRC calculation?

No we are talking about a different algorithm that results in different
results, thats why its important to choose now since we can't change it
later without breaking pg_upgrade in further releases.

http://en.wikipedia.org/wiki/SIMD_%28hash_function%29

Greetings,

Andres Freund

-- Andres Freund	                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services